<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
</html>
<script>
	//上地加下地乘高除2
	var shangdi = 3;
	var xiadi = 8;
	var gao = 5;
	var mianji = ((shangdi+xiadi) * gao) / 2
	document.writeln("面积：(("+shangdi+"+"+xiadi+")*"+gao+"）/2="+mianji);
</script>
